In semiconductor technology it is necessary to produce ever smaller structures on a substrate. So-called extreme ultraviolet (EUV) lithography technology with wavelengths in the soft X-ray range (10-15 nm) is currently being developed for the lithographic patterning of dimensions below 50 nm. One insulation appertaining to this technology is known, e.g., from the article by D. A. Tichenor et al. “System Integration and Performance of the EUV Engineering Test Stand”, Emerging Lithographic Technologies V, Proceedings of SPIE Vol. 4343, pp. 19 to 37, (2001). This article describes the generation of the EUV radiation by means of a xenon plasma.
In the apparatus configuration an influencing device, use is made for example, of multilayer reflection mirrors for illuminator, imaging optical system and mask, in order to capture the emitted radiation. Said multilayer reflection mirrors generally comprise 40 to 50 Mo/Si double layers having a thickness of 6.8 nm in each case, corresponding to half the wavelength of the EUV radiation used.
“Laser Produced Plasma” (LPP) sources and “Discharge Produced Plasma” (DPP) sources are known as radiation sources for generating the plasma (see e.g. Banine and Moors, “Extreme Ultraviolet Sources for Lithography Applications”, Emerging Lithographic Technologies V, Proceedings of SPIE Vol. 4343, pp. 203 to 214, (2001); Lebert et al. “Comparison of Different Source Concepts for EUVL”, Emerging Lithographic Technologies V, Proceedings of SPIE Vol. 4343, pp. 215 to 225, (2001) and Moyer et al. “Laser Produced Plasma (LPP) Scale-up and Commercialization”, Emerging Lithographic Technologies V, Proceedings of SPIE Vol. 4343, pp. 249 to 254, (2001)).
In an evacuated vacuum chamber of the illuminator (also called condenser) that contains the EUV source and condenser mirrors, a substance (usually xenon) is highly ionized by means of a laser pulse (typically Nd:YAG) in the case of an LPP source or by means of an electrical discharge in the case of a DPP source. The plasma is restricted to the laser focal range and emits light in the desired EUV range. The multilayer mirrors of the illuminator, in particular the first condenser mirror, are exposed to bombardment by multiply charged ions.
This gives rise to the problem that, as a result of sputtering and implantation effects, and also as a result of electron and ion assisted deposition and oxidation processes, particularly the mirror devices and the gas outlet nozzles of the plasma sources are damaged considerably during operation of the plasma sources and their service life is limited. Average value and homogeneity of the reflectivity of the mirrors thereby decrease rapidly and the roughness increases. The consequence is high costs owing to the required exchange of the multilayer mirrors (in particular of the first condenser mirror) and of the source components (e.g. nozzles).
Hereto, this problem has been counteracted only by selecting suitable inert materials for the device. The plasma-induced depositions of carbon-containing layers can be compensated for by metered oxidizing additions of, e.g. water or alcohols. In this case, by way of example, the multilayer mirrors must not be damaged by excessive oxidation.
The problem of the known solutions is that the ion bombardment has not been counteracted hereto. The problem thus remains and the device continues to be exposed to ion bombardment and wear.